Question

2) Figure 8.1 displays the reactivity/stability series of carboxylic acid derivatives. In the final step of the reaction sequence you will perform in lab, an amine is converted to an amide using acetic anhydride. Rationalize the relative stability of the four carboxylic acid derivatives shown below by considering the % contribution of each of the resonance structures shown. It may be helpful to use the B3LYP/6-316(d) NBO data provided below via QR codes and on Canvas. (4 pts) Нас H3C^x Resonance Structure ! Resonance Structure 11 Compound % Contribution of l % Contribution of III/II QR code DAD 64% 27% 2.4 H₃C NH₂ 67% 23 % 2.9 HICOH Hoc 78 % 10% 7.8 OH 68 % 4% 17.0 Hoche

Answer 1

of carboxylic acid derivatives Resonance stability is as follows 4 C - her Resonance Resonance Structure-I structure. I When more electonegative atom having lone pair of electron is attached to carbonyl carbon then structure I is more stable because more electronegative atom can nor gives a lone pair to carbonyl carbon easily re. de localization I is not occure easily When less electronegative atom having lone pair of electon is attached to carbonyl carbon then delocalization occure & Structure I percentage increases.

@ In case of amide (he th NH2) is more because nitrogen lone given. delocalisation pair easily Sünin 1644 271) h on no 237 1677 so percentage 1 Here or oxygen is more electronegative de localisation is less. a la nola e 1 10% • In case of acyl chloride & acyl bromide de locali - sation of lone pair is very less because these atoms are more elecbo negative. more electronegative asom can not delocalised ik Jone pair through conjugation.

Date Page 6 The compound in which percentage of resonance structure I is more than structure I the carbon of carbonyl is more electron deficient in such Compound such compounds undergo substitution freaction faster. Here acyl chloride & acyl bromide have high percentage of structure I so they undergo fast substitution reaction. Amine + Acetic anhydride - Amide R-NH2 & R RM o R Acetic anhydride TR=ch + R-don non acid Amine Amide